A technology for coating an antireflection film on the surface of an optical lens such as a spectacles plastic lens by utilizing the sputtering has been proposed in recent years. The sputtering which is one of film forming method of the semiconductor technology is anticipated to improve the productivity in forming a thin film on the surface of an optical lens and the performance of the lens. Normally, a plurality of optical lens base materials are set on a circular planar holder (a substrate holder or a lens tray) and the holder is rotated in performing the process for depositing the film on the surface of the optical lens by means of the sputtering.
Conventionally, thickness of a film deposited by utilizing the sputtering has been considered to be well distributed. However, the distribution of thickness of the film must be more accurate and uniform in utilizing the sputtering to deposit the thin film onto the optical lens.
Rigorous uniformity is required as for the thickness of the film in particular in depositing an antireflection film on the surface of the optical lens by utilizing the sputtering. When the thickness of the antireflection film on the surface of the lens is not uniform, interference color varies, thus dropping the wearing feeling and the commercial value of the optical lens.
Further, in case of a spectacles lens for example among the optical lenses, the lens has a meniscus shape, whose one surface is concave and the other surface is convex, and the both surfaces have curvatures, respectively. In depositing the antireflection films on the surfaces of the spectacles lens by using the sputtering, normally the spectacles lens is arranged horizontally on a holder and upper and lower targets are disposed so as to face to the both sides of the spectacles lens, respectively, to perform the sputtering on the both sides at the same time. When the lens edge thickness of the spectacles lens is large at the concave surface in particular in that case, oblique incidence of sputtered particles to the peripheral part of the lens increases and the thickness of the film at the lens peripheral part becomes larger than the thickness thereof at the lens center part because distance where the sputtered particles fly and arrive is different due to the difference in curvature. When the lens edge thickness of the spectacles lens is small and when a member which blocks the lens peripheral part exists, non-uniformity of thickness occurs at the blocked part of the lens peripheral part.
An object of the present invention is to meet the above-mentioned requirements and to solve the above-mentioned problems, and is to provide a mechanism for setting the optical lens base materials on a holder, which allows the thickness of the film to be almost equalized at the center part and the peripheral part of the lens and the distribution of the film thickness to be equalized on the surface in depositing the thin film on the surface of the optical lens base material by means of the sputtering.